In the related art, as a container which contents can be easily stored in and taken out from, there has been widely used a capped container with a cap that closes an opening that has been formed at a head section of a container body. In many cases, a capped container includes fixing means for a container body and a cap such that the cap can be easily opened and closed, while preventing contents that have been stored in the container body from leaking outside during storage or transportation when the cap is closed. In particular, for contents that are likely to scatter, such as liquids, a reliable fastening means is required, and a method using screws, for example, is generally known.
In a case where a container and a cap are fastened using screws, screw positions of a screw that has been provided outside an opening of the container and an inner screw to be threadedly engaged with the outside screw are adjusted inside the cap, and either the container or the cap is rotated in a certain direction. Then, screw threads are guided by screw grooves to move in a circumferential direction. As a result, the cap and the container are fastened while moving in an axial direction. In order to maintain airtightness inside the container, the inside of the container is generally separated from outside and sealed by arranging a packing material in part of a contact part of the two members and threadedly engaging the cap with the container body (not illustrated).
However, in a case where a cap is fastened only with a fastening structure by screws, when vibration or the like is applied to a container after fastening, friction resistance of the screws decreases by the vibration, and the fastening structure of the container and the cap loosens, which results in deterioration of sealing performance thereof, and in some cases, a risk that the cap may come off.
Therefore, in order to increase loosening and friction of the screws, known is a structure that increases friction force by fastening the screws, prevents loosening of the screws, and improves adhesive performance by arranging a plurality of screw threads with different lead angles (Patent Literature 1). Another structure known has, in addition to the fastening means by screws, a means for locking and firmly attaching a container by entrance and adherence of a projection shape annular projection of the container into a recess section provided on an edge side of the cap, or by either projection section's climbing over the other, due to elastic deformation caused by a certain pressure in an axial direction in either a cap section or a container body, or both thereof. There have been proposed capped containers with a locking means by projections in addition to the screw means, such as those with a mechanism that prevents a screw from returning at a terminal end of the screw by installing a projection shape locking tool at a terminal end of a screwing section (Patent Literature 4), those that include an annular projection at a terminal end of a screwing section and prevent the screw from loosening due to easy return thereof, by climbing over the annular projection by an annular projection in a cap section by screwing the cap (Patent Literatures 2 and 3), and those that can, as a result of this, prevent loosening of the cap as well as occurrence of a backlash (Patent Literature 5). However, for example, in a case where the contents are liquids, or in a case where a specific gravity thereof is large, there is a problem that the contents overflow when opening by being blown up near the cap by, for example, vibrations applied from outside.
As a means for preventing such leakage, it may be acceptable to include a method using a double cap or a means such as installing inside the cap an inner ring, the diameter of which is smaller than that of a container body. However, in a case where a double cap is used, overflow of the contents can be prevented, whereas, in a work requiring quick movement in an experiment, for example, removing, after opening a cap, another cap is a complicated work. Even in a method using an inner ring, a gap often generates between the container and the inner ring, which may deteriorate adhesive performance.
Then, the applicant has proposed a capped container, by which sealing performance inside the container is sufficiently maintained, while fastening a cap and the container by a simple fastening structure (JP 2014-997).
The capped container the applicant has proposed includes, as illustrated in FIGS. 1(a) and 1(b), a container body 1 and a cap 2. The container body has outer screws 12 formed on an outer peripheral surface 111 of a head section 11. The cap has inner screws 22 to be threadedly engaged with the outer screws 12, formed on an inner peripheral surface 21, and is placed on the head section 11 of the container body 1 by screw-fitting and removed therefrom. An opening end 112 in the head section 11 of the container body 1 closely contacts a top inner surface 24 of the cap 2, when the cap 2 is placed on the head section 11 of the container body 1. A so-called clickstop mechanism is provided, where, for the container body, a container body-side annular projection 13 is projected toward a top section rather than in a terminal end section of the outer screws 12 on the outer peripheral surface 111 of the head section 11, and on a top section side rather than in a terminal end of a top section side of the inner screws 22 on the inner peripheral surface of the cap 2, a cap-side annular projection 23 is included, which can be climbed over by the container body-side annular projection 13 and is interengaged therewith at the climbing-over position at the time of threaded engagement with and placement on the head section 11 of the container body 1. By including the fastening means by screws and annular projections, the cap can be reliably fastened to the container body by one click. Compared with a conventional capped container, not only sealing performance is superior, but also opening and closing operation of the cap is simple due to one-click operability. Like a container used for temporarily storing collected samples (such as tumor, blood, and tissue), in fields such as medical and research, it is, due to the nature, required to prevent contamination with bacteria, chemical substances, and the like from outside, or prevent, for example, biological hazards caused by scatter of collected samples to the outside. Therefore, high sealing performance is required, while in terms of test operability it is most appropriate to use as a container with a cap easy to open and close, for example.
However, in the capped container the applicant has proposed, there is a possibility that the cap comes off at least when a force that causes a cap-side annular projection to climb over a container body-side annular projection is applied, in a case, for example, where containers, supporting members, and the like adjacently arranged fly in a vertical direction, collide with lower end surfaces of the caps placed on the container bodies, and receive an unexpectedly large impact in a direction of the top section of the cap, in a case, for example, where a plurality of capped containers is packaged in an erected state and transported under an enormous specific gravity during transportation by airplane, for example. In order to prevent this sort of problem, it is possible to strengthen engagement between the cap-side annular projection and the container body-side annular projection, that is, to make height higher and increase force to climb over, but there is a problem that opening and closing operation becomes difficult, thereby losing convenience.